Project Description Malaria has profoundly affected human lives for thousands of years and remains one of the most serious, life- threatening infectious diseases, causing nearly 0.5 million deaths in 2015. The effectiveness of artemisinin- based combination therapies has led to declines in malaria-related deaths. However, the emergence of artemisinin-resistant parasites in SE Asia poses a serious threat to malaria control programs, necessitating that a robust pipeline be supported for the discovery of new drug therapies. This urgent need is fostered by Medicines for Malaria Venture (MMV), which supports projects from early discovery work to clinical trials. Through a NIH/MMV funded project our team clinically validated dihydroorotate dehydrogenase (DHODH) as a new target for the treatment of malaria. DHODH inhibitors have since emerged as important players in the malaria drug discovery portfolio, providing both blood and liver stage activity, and long human half-life that supports single dose cure or once weekly chemoprevention. In past fund periods, we identified the triazolopyrimidine DSM265 by a target-based high throughput screen (HTS) followed by a structure-based lead optimization program. DSM265 is currently in clinical development and was found to be efficacious in a single dose for the treatment of P. falciparum patients in Peru. However, several liabilities have emerged, including lower P. vivax activity, which represent areas for improvement in next generation candidates targeting DHODH. To that end in the last grant period we identified and advanced a backup compound (DSM421) from the same series; however, development of DSM421 was put on hold due to toxicity issues identified in preclinical studies. Thus, despite the success of our program it is essential that we identify DHODH inhibitors from novel structural classes that overcome the known liabilities of DSM265 if for any reason it fails to make it to registration. Different classes of DHODH inhibitors could potentially also be useful for different product profiles within the portfolio. With these goals in mind, we are currently optimizing a pyrrole series identified in our original HTS. We have identified potent and selective analogs that do not share cross-resistance with DSM265 and which have equivalent P. falciparum and P. vivax activity. Further lead optimization to improve metabolic stability is underway. We have also identified a number of other leads by scaffold hopping that are positioned to enter full-scale optimization. Our team has worked together successfully throughout the development of DSM265/DSM421. We have the expertise to carry out the full range of lead optimization activities, including medicinal chemistry, X-ray structure determination, structure- based modeling through a collaboration with Schrodinger, enzyme and cell-based assays, pharmacokinetics and metabolism studies. Additionally, MMV will provide extra financial support in key areas and will provide project management, oversight and advisors to further facilitate the project. Successful completion of our aims will identify novel DHODH inhibitors with the potential to be advanced for the treatment of malaria.